Joining system head, joining system, and method of feeding and joining elements

ABSTRACT

A joining system head ( 22 ) is proposed for fixation to a movable frame ( 12 ), in particular to a robot ( 12 ), having  
     a holding means ( 66 ) for an element ( 36 ) to be joined to a part ( 38 ),  
     a joining drive means ( 64 ) to move the holding means ( 66 ) along a joining direction ( 40 ) for joining, and  
     a feeding means ( 44 ) for feeding elements ( 36 ) to the joining system head ( 22 ). Here a control means ( 42 ) to control the joining drive means ( 64 ) is arranged at the joining system head ( 22 ) spatially distanced from the holding means ( 66 ) and the joining drive means ( 64 ), so that the holding means ( 66 ) and the joining drive means ( 64 ) form a joining tool ( 32 ) of small dimensions, and means (68) are provided to pass on the elements ( 36 ) fed to a transfer station ( 46 ) of the feeding means ( 44 ) in each instance to the holding means ( 66 ) from in front.

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to a joining system head forattachment to a movable frame, in particular to a robot, having

[0002] A holding means for an element to be joined to a part, and

[0003] A joining drive means to move the holding means along a joiningdirection for joining.

[0004] A feeding means for feeding elements to the joining system head.The present invention relates further to a joining system having a robotmovable on at least two coordinate axes and a joining system headattached to the robot. Lastly, the present invention relates to a methodof feeding elements from a stationary unit to a movable joining systemhead and joining said elements to parts by means of the joining systemhead.

[0005] Such a joining system head, such a joining system and such amethod of feeding and joining elements by means of a joining system headare generally known. The term ‘joining’ in the present context isintended to refer to all ways of connecting elements to parts, inparticular connections of metal elements to metal parts, for example bybonding, forming, as for example riveting, or by union of matter, as forexample welding, including short-time arc welding. Short-time arcwelding is often referred to as bolt welding, even though it is notexclusively bolts that are welded. A current system of bolt welding inindustrial use, in combination with a robot, is known in the brochure“Neue TUCKER Technologie. Bolzenschweiβen mit System!,” Emhart TUCKER,9/99.

[0006] Bolt welding finds application chiefly, but not exclusively, invehicular technology. Here, metal elements such as metal bolts, with orwithout threads, eyes, nuts etc., are welded onto the sheet metal of thebodywork. The metal elements then serve as anchors, or fasteningelements, to fix for example interior fittings, lines and the like tothe sheet metal of the body. At the joining system head, disclosed inthe above-mentioned Emhart TUCKER publication, the joining drive meansis configured either as a linear electric motor or as a combination of alift magnet and a spring.

[0007] The holding means is constituted by a one-piece tongs elasticallyexpandable in radial direction. The elements are as a rule welding boltscomprising a head having a somewhat larger diameter than the shank ofthe bolt. In the known system, the bolts are fed to the welding head byway of suitable feeding conduits by means of compressed air. The boltsare thus fed ‘head first’ into the tongs from behind. Ordinarily thebolt will strike the tongs from the inside, but without passing throughit. A loading pin provided coaxial with the tongs is then actuated topropel the bolt thus fed through the tongs. The tongs are elasticallyexpanded radially when the head of the bolt passes through. Then thetongs snap closed elastically around the shank of the bolt and hold itfast in the position determined by the travel of the pin.

[0008] The joining drive means in the form of a linear motor (or liftmagnet/spring combination) has a travel of a few millimeters. Also, thewelding head is fixed at the end of an arm of the robot, usually by wayof a pneumatic or hydraulic carriage. That is, the entire welding headis movable in a direction parallel to the welding axis by means of thecarriage, which has a considerably greater travel than the linear motor.The welding head further comprises a control means to control the linearmotor and the loading pin, provided spatially separate from the weldinghead, more specifically in a stationary feeder.

[0009] To perform a welding operation, first the robot is programmed sothat it travels into a predetermined position in which the carriage andlinear motor axes are perpendicular to the sheet metal onto which thebolt is to be welded. The bolt is prestressed so that it protrudesvis-à-vis a supporting foot. Then the carriage is actuated until thefoot meets the sheet metal. The bolt held in the holding means thenrests in contact with the sheet metal. Next comes a determination of thezero line of the holding means with respect to the sheet metal.Alternatively, however, there are methods of zero line determinationthat dispense with the supporting foot.

[0010] Then, in the case of welding with supporting foot, an electricpre-current is switched on, passing through the bolt and the part. Thebolt is then lifted relative to the part by means of the linear motor(lifting means). An electric arc is set up. Then a switch is made to thewelding current. By the high welding current, the opposed faces of boltand part begin to be fused. The bolt is then lowered onto the partagain, so that the respective melts will mingle. Upon attainment of thepart and the short circuit of the arc, or just before, the weldingcurrent is switched off. The entire melt solidifies and the weldedconnection is complete.

[0011] Now the welding head is drawn off from the welded-on bolt, usingthe carriage. The carriage is necessary because, among other reasons,the drawing-off motion must take place exactly on the centerline of thewelded-on bolt. Otherwise, owing to the one-piece tongs, there would bedanger of damage to the bolt and/or the tongs. The robot arm alone isnot capable of such a precise linear motion in an arbitrary direction ofspace. For owing to the superposition of the simultaneous regulation ofseveral components of robot arm motion, as required for this purpose,such linear motions can be executed by the robot with a certain amountof undulation only. The known welding head comprises a comparativelygreat axial extent. Since moreover the welding head must be drawn offfrom the bolt in axial direction, use of the welding head in places ofdifficult access is possible only within limits.

[0012] Then there are developments for employing robot technology tofeed the bolt. Here a separate pick-up takes pre-sorted bolts and bringsthem to the welding location. This is disclosed in “Bolzenschweiβen.Grundlagen und Anwendung” by Trillmich, Welz, FachbuchreiheSchweiβtechnik, DVS Verlag, 1997, Chapter 9.3. It is there explainedthat this technology lends itself especially to headed bolts that,because of their size and shape, cannot be blown through hoses. Thistype is referred to as the “pick-up system.”

[0013] Further, a welding head by the firm of Nelson has been disclosed,in which a lift device moves a carrier projecting laterally arm-like upand down. At the terminal portion of the carrier, a holding means withtongs is rigidly mounted. The bolts are fed, as in the case of theTUCKER welding head described above, to the tongs from behind, by meansof a compressed air hose extending through the carrier. The end portionof the carrier with holding device fixed thereto is more readilypositioned at inaccessible locations. The lift device to move theprojecting arm and the pertinent control means are arranged in theinitial portion of the carrier.

[0014] Against this background, the object of the invention consists inspecifying an improved joining system head, an improved joining systemand an improved method of feeding and joining fed elements. This objectis accomplished, for the joining system head initially mentioned, inthat a control means to control the joining drive means is arranged atthe joining system head spatially separate from the holding means andthe joining drive means, so that the holding means and the joining drivemeans form a joining tool of small dimensions, and in that means areprovided to pass on the elements fed to a transfer station of thefeeding means to the holding means in front in each instance.

[0015] The joining system head according to the invention represents acompletely novel concept. This is based on two fundamental ideas. One ofthese ideas consists in providing the control means at the joiningsystem head, but spatially distanced from the holding means and thejoining drive means. The holding means and the joining drive means canconsequently form a joining tool of small dimensions and not muchinterference edge relevance. The other idea consists in feeding theelements by means of the feeding means, not immediately all the way tothe holding means, but as far as a transfer station likewise distancedfrom the joining tool. In addition, means are provided to pass on eachof the elements fed to the transfer station to the holding means from infront. In this way it is possible to keep the over-all axial length ofthe joining tool small, since no loading pin is required to position theelements through the holding means from behind.

[0016] Since the joining drive means and the holding means areintegrated into a joining tool, no transmission of a lifting motion overlong distances (cantilever arm or the like) is needed. Consequently thepositioning and the actual joining or welding can take place locallywith high precision. In the joining system according to the invention,the above object is accomplished in that a joining system head accordingto the invention is fixed to the robot arm.

[0017] The method according to the invention for feeding elements from astationary unit to a movable joining system head and joining fedelements to parts by means of the joining system head contains the stepsof feeding an element from the stationary unit to the movable joiningsystem head while the joining system head is joining an already fedelement to a part. According to the invention, the elements are notconveyed from the stationary unit all the way to the holding means inone step as in the prior art. Instead, the elements are at first fedfrom the stationary unit only as far as the transfer means. This feedingstep can accordingly take place while the joining welding head itself isjoining an already fed element to a part. By virtue of this partialprocessing, shorter cycle times are obtainable over all. The object hasthus been completely accomplished.

[0018] It is of especial advantage if the joining tool is mounted on anend portion of a projecting elongated carrier. The spatial distancebetween joining tool and control means is consequently attained by theelongated carrier. This makes it possible to bring the joining tool toinaccessible locations through openings.

[0019] Here it is especially preferred if the joining tool is movablymounted on the end portion of the carrier and if a loading drive meansis designed to move the joining tool to the transfer station in order topass an element on to the holding means. In this embodiment, it isespecially advantageous that the movable mounting of the joining toolcreates an additional degree of freedom for positioning the same. Forexample, the joining tool, when it has already been introduced into acavity by means of the carrier, can still be moved. This permitsflexible “handling.” Further, the movable mounting of the joining toolmakes it possible for the means of passing an element on from thetransfer station to be realized by the mobility of the joining tool. Thejoining tool consequently in each instance itself ‘fetches’ the elementsto be joined from the transfer station.

[0020] Further, it is preferred in this embodiment if the joining toolis rotatably mounted on the end portion of the carrier and if theloading drive means is designed to rotate the joining tool as far as thetransfer station. A rotatability of the joining tool on an end portionof the carrier is comparatively simple to achieve as a matter of design.Rotatability as a single degree of freedom is sufficient for numerousapplications. When it is considered that the carrier itself is alsorotatable about its lengthwise axis by means of the robot as a rule, andarbitrarily positionable in space, joining operations can be carried outeven in highly inaccessible locations. The interference edge profile ofthe joining tool is determined by the necessary radius of swing.

[0021] The loading drive means serves generally, in the first place, tofetch one element at a time from the transfer station, and in the secondplace, also to position the joining tool relative to the carrier in awelding position. It will be understood that the variability will begreater the greater the angular range within which welding positions canbe arranged by the loading drive means.

[0022] According to an alternative embodiment, the loading drive meanscomprises a motor arranged at the end portion of the carrier. In thisembodiment, a precise control of the joining tool can be achieved withgood response behavior.

[0023] In an alternative embodiment, the loading drive means comprises amotor arranged in the neighborhood of the control means and atransmission that transmits motions of the motor to the joining tool. Inthis embodiment, an improved interference edge clearance results, sincethe interference-edge relevant end portion of the carrier does notcomprise any motor of its own to move the joining tool. Rather, thecomparatively bulky motor is arranged in the neighborhood of the controlmeans and transmits its motion to the joining tool by way of atransmission.

[0024] Here it is especially preferred if the motor is a rotary motor,in particular an electric motor, and if the transmission is atransmission with tension means. With a rotary motor, motions can beexecuted precisely and with high responsiveness. With the tensiontransmission, comparatively great distances between the neighborhood ofthe control means on the one hand and the end portion of the carrier onthe other hand can be achieved by comparatively simple design.

[0025] Upon the whole, it is of advantage if the joining drive meansconsists of a linear electric motor. In this embodiment, the joiningdrive means is configured as a lift means. A linear electric motorrequires only relatively few lines to trigger it, and can be regulatedin both lift directions.

[0026] Here it is of especial advantage if the longitudinal axis of thejoining drive means and the longitudinal axis of the holding means aredistanced parallel to each other. In this embodiment, it is possible soto position the holding means that even welding positions close to edgesare attainable. The distance between the longitudinal axes may be in therange of some few centimeters, just enough to shift the holding meansout of the projection of the joining drive means in joining direction.

[0027] According to a further preferred embodiment, the holding meanscomprises a plurality of jaws arranged distributed around thelongitudinal axis of the holding means and movable towards and away fromeach other, in order to hold or release an element, according to thecase. Here it is especially preferred if the holding means comprises twojaws. The term ‘jaws’ in the present context is to be understoodbroadly. The jaws may for example be elongated fingers. With twofingers, rotationally symmetrical or approximately rotationallysymmetrical parts in particular can be grasped with comparativeconvenience and held securely.

[0028] It is preferred if the jaws are movable far enough away from eachother so that the holding means can release the element by being drawnoff from the element oblique to the joining direction. This embodimentmakes it possible to perform the operation of ‘withdrawing’ the joiningsystem head from the element joined to the part by means of the robotalone. A carriage for guiding a completely rectilinear return motion isthen not required. In that sense, this embodiment also contributes to asmaller axial extent of the welding head.

[0029] It is especially preferred, however, if the jaws are movable farenough away from each other so that the holding means can release theelement by being swung away from the element about an axis of rotationoriented transverse to the joining direction. In this embodiment, thejaws can be moved away from each other far enough so that the joiningtool need not be withdrawn in joining direction. Rather, it is possibleafter the joining operation to withdraw the joining tool transverse, inparticular perpendicular, to the joining direction, the element beingpassed between the jaws of the holding means. In this embodiment,consequently, no axial motion is required.

[0030] In this way it is possible to pass the carrier with joining toolarranged on the anterior end portion through even extremely smallopenings, and execute joining operations inside of cavities. Thecarrier, after attaining the joining position, can remain positionedalmost without change. After the joining operation, the joining tool ismoved, in particular swung, away transverse to the joining direction,and then the carrier can be withdrawn from the cavity again along itslongitudinal axis.

[0031] Further, this embodiment makes it possible for the elements to begrasped in especially simple manner by the transfer station. The joiningtool is so moved, in particular swung, in this embodiment, that theholding means with released jaws is aligned with an element at thetransfer station. Then the element is grasped by the jaws, and taken outof the transfer station by a motion, in particular a swinging motion.

[0032] In general, it is preferred if a jaw actuator is provided,actively opening and/or closing the jaws. In this embodiment, as a rulethe jaws are configured as rigid fingers. The jaw actuator ensures thatthe jaws are either actively opened, to release an element, or elseactively closed, to hold the element.

[0033] Alternatively to this, it is possible to configure or mount thejaws elastically, so that they are passively movable towards and/or awayfrom each other. In this embodiment, the jaws may either be made of anelastic material, in which case other elastic means are superfluous as arule, or else the jaws may be configured as rigid elements andelastically mounted. It is also possible, within the scope of thisembodiment, for the jaws to be elastically pre-stressed, either inholding or in releasing direction. In that case, as a rule an actuatoris provided, which actively moves the jaws in the respective otherdirection.

[0034] In general, in an especially preferred embodiment, the transferstation is arranged on the longitudinal carrier. In this way it ispossible to achieve a fixed relative position of the transfer stationwith respect to the joining tool. Besides, it is advantageous for thecross section of the carrier to be smaller as a rule than the crosssection of the joining tool, so that space will be available for thetransfer station.

[0035] Further, it is generally of advantage if the feeding meanscomprises a magazine for elements. In this way, it is possible always toplace an element in readiness to be ‘grasped’ at the transfer station.

[0036] In the joining system according to the invention it is ofadvantage if a stationary individuating means conveys individualelements all the way to the transfer station of the joining weldinghead. This embodiment serves in general to enhance the degree ofautomation. Such stationary individuating and feeding means are knownper se in the prior art. However, they convey individuated elements allthe way to the holding means in one step, whereas in the joining systemaccording to the invention, a conveyance takes place only as far as thefeeding means (transfer station). Thence the holding means ‘fetches’ anelement conveyed thither. It will be understood that the featuresmentioned above and those yet to be illustrated may be employed not onlyin the combination specified in each instance but also in othercombinations or by themselves, without departing from the scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the invention are represented in the drawing byway of example and will be illustrated in more detail in the descriptionto follow. In the drawing,

[0038]FIG. 1 shows a schematic view of a joining system according to theinvention;

[0039]FIG. 2 shows an alternative conformation of a joining systemaccording to the invention;

[0040]FIG. 3 shows a longitudinal section of an embodiment of a holdingmeans;

[0041]FIG. 4 shows a cross-section at the line IV-IV in FIG. 3;

[0042]FIG. 5 shows the end portion of a joining system head according tothe invention, with an alternative conformation of a joining tool;

[0043]FIG. 6 shows a view of the end portion of the joining system headof FIG. 5 from below;

[0044]FIG. 7 shows another alternative embodiment of a joining tool of ajoining system head according to the invention;

[0045]FIG. 8 shows a schematic representation of a transfer station of ajoining system head according to the invention;

[0046]FIG. 9 shows a schematic representation of an alternative transferstation of a joining system head according to the invention;

[0047]FIG. 10 shows a schematic representation of still anotheralternative embodiment of a transfer station of a joining system headaccording to the invention;

[0048]FIG. 11 shows a schematic sectional view at the line XI-XI in FIG.10; and,

[0049]FIG. 12 shows a schematic side view of an alternative embodimentof a joining system head according to the invention.

DETAILED DESCRIPTION

[0050] In FIG. 1, a joining system according to the invention isgenerally designated 10. The joining system 10 comprises a robot 12. Therobot 12 contains a stationary base 14 from which two arms 16, 18extend, articulately connected to each other. At the end of the arm 18,a flange 20 is provided.

[0051] To the flange 20, a joining system head is attached, generallydesignated 22 in FIG. 1. The joining system head 22 comprises abaseplate 24 attached to the flange. From the baseplate 24, an elongatedcarrier 26 extends. The elongated carrier 26 comprises a first shortcarrying segment 28 and an adjoining second elongated carrying segment30. The second carrying segment 30 is bent off from the first carryingsegment 28 by an angle α of 120°. The angle α is preferably between 60°and 80° or between 100° and 120°. In general, however, it is alsoconceivable that the first carrying segment 28 and the second carryingsegment 30 may be oriented on an axis with each other. The axis of thesecond carrying segment 30 is designated 27 in FIG. 1.

[0052] At the end of the second carrying segment 30, a joining tool 32is mounted rotatable about an axis 34. The axis of rotation 34 extendsperpendicular to the axis 27 of the second carrying segment 30 and, inthe embodiment shown, is oriented about parallel to the baseplate 24.

[0053] The joining tool 32 serves to weld an element, in particular awelding bolt 36, to a part, in particular a metal sheet 38. Although thejoining system may be employed for numerous kinds of joining as a matterof design, a conformation of the joining system as a bolt-weldingsystem, or short-time arc-welding system with lift ignition, isespecially preferred. In the following, therefore, without loss ofgenerality, the joining system will be referred to as a bolt weldingsystem and the joining system head 22 as a bolt welding head. Thejoining tool 32 will be referred to as a welding tool 32. The weldingtool 32 welds the bolts 36 to the part 38 in a linear motion (joiningdirection 40).

[0054] The welding head 22 further comprises a control means 42. Thecontrol means 42 is provided at the initial portion of the elongatedcarrier 26 and, in the embodiment shown, is mounted on the firstcarrying segment 28, to wit next to the baseplate 24. The control means42 serves to drive the joining tool 32 and as intersection withsuperordinate control devices.

[0055] The welding head 22 further comprises a feeding means 44. Thefeeding means 44 serves to pick up bolts by the shank in advance from afeed hose and place them in readiness at a transfer station 46. The feedmeans 44 is consequently configured essentially as a tube or hose andextends along the elongated carrier 26. The transfer station 46 islocated in a mid-portion of the second carrying segment 30. In it, oneelement at a time is placed in readiness for transfer to the weldingtool 32. This element is designated 36″ in FIG. 1.

[0056] The welding system 10 further comprises a stationary base station50. The base station 50 serves to furnish energy for welding to thewelding head 22 and serves as superordinate control device. The basestation 50 is connected to an individualizing device 52. Theindividualizing device 52 serves to individualize bolts, as a rulesupplied in bulk, and convey them to the feeding means 44 individuallyby way of a hose 54. For this purpose, the individualizing device 52 asa rule comprises a compressed air unit to convey the elements 36pneumatically.

[0057] Further, FIG. 1 shows a line 56 connecting the base station 50 tothe welding head 22. The line 56 is generally embodied as a system oflines, and includes lines to carry the welding current, control linesetc. Further, FIG. 1 shows a line 58 connecting the welding head 22 tothe base 14 of the robot 12. The line 58 is optionally provided andcontains one or more control lines. By means of the control lines 58,the motions of the robot 12 can be matched with those of the weldingtool 32.

[0058] Alternatively or additionally, the base 14 of the robot 12 isconnected to the base station 50 by way of a line 60. Hence it ispossible also for the matching to take place between robot 12 andwelding head 22 by way of lines 60, 56. The lines 56, 58 are passed tothe control means 42, whence some are looped to the welding tool 32 (forenergy supply to unit there), others are utilized directly.

[0059] The welding tool 32 comprises a housing 62 rotatably mounted onthe axis 34. At the housing 62, a joining drive means 64 is provided inthe form of a linear motor 64. The linear motor 64 serves to move aholding means 66 projecting from the housing 62 perpendicular to theaxis of rotation 34 for holding one bolt 36 at a time. The linear motor64 therefore constitutes a lifting means for executing lift and dipmotions in the course of a bolt welding operation, as described in theintroduction.

[0060] Further, at the end portion of the second carrying segment 30, arotary drive 68 is provided, serving to rotate the welding tool 32 undercontrol into any angular positions in relation to the second carryingsegment 30. The rotational range is typically at least 270°, commonly360°. The rotary drive 68 serves firstly to rotate the welding tool 32into a suitable welding position in each instance, one of which weldingpositions is shown in solid lines in FIG. 1. An alternative weldingposition is indicated by dot-dash lines at 32′. In the further weldingposition, the welding tool 32′ is employed along a welding direction 40′to weld a bolt 36′ to a part not explicitly shown.

[0061] Further, the rotary drive 68 serves as loading drive means. Forthis purpose, the welding tool 32 is turned into a position shown dottedin FIG. 1. In this position, the holding means 66″ is oriented flushwith the transfer station 46, and is able in that position to grasp abolt 36″ there held in readiness and take it over for a subsequentwelding operation.

[0062] Although, in the embodiment represented, the loading drive meansis constituted by the rotary drive 68 alone, for example an electricmotor, modifications of this are conceivable. Thus the loading drivemeans may for example be constituted in that the—non-rotatable—weldingtool 32 is shifted in lengthwise direction on the carrier 26, to mentionone example. It will be understood that then the transfer station 46would have to be arranged correspondingly in a different place.

[0063] It is easily seen that the welding tool 32 may be configured withvery small dimensions. In the first place, the welding tool 32 isspatially separated from the control means 42. In the second place, thewelding tool 32 is decoupled from the pneumatic bolt-feeding means. Sono pneumatic or hydraulic lines need be flanged to the welding tool 32.The supply of electricity to the linear motor 64 and/or the rotary drive68 is comparatively easy to arrange. The same applies to the actuationof the holding means 66, insofar as it is actively actuatedelectrically.

[0064] Since the bolts 36 are put into the holding means 66, not frombehind but from in front, no loading pin is required as in the priorart. Therefore the welding tool 32 can be compact in axial direction. Itwill be understood that instead of a linear motor as joining drive means64, alternatively a combination of a spring and a solenoid may beprovided. Further, it will be understood that the rotary drive 68 may beconfigured as an electric step motor having a precision of <1°, betteryet 0.5°.

[0065] The parameters assigned to the rotary motion relate firstly to awelding program and secondly to a program of robot motion. Each weldingposition has its own welding program and its own robot motion program.By referring the parametric data to the several welding and robot motionprograms, it is ensured that firstly the bolt 36 will always beperpendicular to the surface of the part 38, and secondly the weldingtool 32 will be in a position in the robot motion affording the robotmaximal freedom of motion on the way to the welding position. Thecontrol of the rotary motion of the welding tool 32 may be effected byway of the base station 50 and/or by way of the base 14 of the robot 12.

[0066] The oblique angling of the second carrying segment 30 withrespect to the first carrying segment 28 offers, firstly, an improvedinterference edge clearance. Secondly, the feeding means 44 is easier toconstruct, since the bolts, as shown, are held at the transfer station46 by gravity and/or blown air.

[0067]FIG. 1 further shows that the part 38 has the conformation of anangle part having a relatively small aperture 70. Viewed from the robot12, the desired welding position is located inside of a cavity 72. It iseasily seen that the bolt welding system 10 according to the inventionis quite especially well-suited to accomplish this object. To introducethe second carrying segment 30 through the opening 70, the welding tool32 can be turned into a position in which it is largely flush with thesecond carrying segment 30, for example the position 32″ in FIG. 1.

[0068] After introduction into the cavity 72, the welding tool 32 isturned into the welding position indicated by solid lines. Before that,a bolt 36 is picked up from the transfer station 46, so that it islocated in the holding means 66. Then, in per se conventional manner, abolt welding operation is carried out, as explained in the introduction.

[0069] As remains to be set forth in detail below, the holding means 66is preferably of such configuration that it can release the welded-onbolt 36 in a direction transverse to the welding direction 40.Consequently, it is possible to turn the joining tool 32 immediatelyafter welding back into the flush position 32″, with no need for thesecond carrying segment 30 to execute a motion in the welding direction40. As soon as the flush position 32″ has been reached, the secondcarrying segment 30 can be withdrawn again through the opening 70. Therobot 12 then carries the welding head 22 to the next welding position.The axis of rotation 34 constitutes an additional axis of rotation forthe robot 12. Hence the positioning in a welding position can beaccomplished in simpler manner. This the more so as the additional axisof rotation is located near the welding position.

[0070] Another advantage of the welding system 10 according to theinvention results as follows. In the prior art, the welding head as awhole was interference-edge relevant. In the prior art, therefore, nopneumatic valves were provided on the welding head. But this occasionedvery complicated cabling between the base station 50 and the weldinghead 22.

[0071] Owing to the spatial separation of the control means 42 from thewelding tool 32 at the welding head 22, the control means 42 itself isnot interference-edge relevant. Consequently valves can be integratedinto the control means 42 at the welding head 22, so that the number andcomplexity of the supply lines can be reduced. Since the control means42 is provided at the welding head 22, no great outlay of electriccabling is needed between welding head 22 and base station 50. Forexample, it is possible for the supply lines 56 in a hose pack tocontain only a welding cable, two auxiliary voltage supplies for thelinear motor and a 24-volt supply for the control means, two lightguides for serial transmission of measurement and control data and thefeed hose 54. In an enlarged version, the hose pack might besupplemented by a protective gas supply line and/or a jet-suction line,for example for color marking. Hence the hose pack can be lighter inweight, torsionally less rigid and therefore more secure.

[0072] Besides, the uncoupling of supply means 44 and welding tool 32makes it possible for the bolts 36 to be fed to the transfer station 46parallel with the bolt welding operation. In the prior art, bolt feedingand bolt welding are strictly serial. Therefore cycle periods of <1second are attainable only with great difficulty and under specialboundary conditions.

[0073] According to the invention, immediately after removal of a boltfrom the transfer station 46 to initiate a bolt welding operation,another bolt can be conveyed from the individualizing device 52 by wayof hose 54 and feed means 44, to the transfer station 46. This can beaccomplished while the welding tool 32 is performing a bolt weldingoperation.

[0074] Also, as the carrier 26 moves from one welding position to thenext, the welding tool 32 can be swung to the transfer station 46 andthen swung into the right setting for the new welding position. Thisparallelism also generally ensures that welding cycle periods ofdefinitely less than 1 second are attainable. Although the elements tobe welded may basically be of any shape, yet elements feedable by meansof compressed air, in particular rotationally symmetrical elements, areespecially suitable for processing by the joining system according tothe invention. The further welding position 32′ may for example be anoverhead position, like the position 32′ shown. This can be attainedwithout need to rotate the carrier 26. This avoids overstraining thesupply cable and hoses.

[0075] In the following description and details and modifications of thejoining system shown in FIG. 1, like or similar elements are designatedby the same reference numerals. Identical designation generally implieslike or similar mode of operation, unless expressly otherwise notedbelow. Where individual elements of the joining system are discussed, itmay be assumed that the function is otherwise identical or similar tothe function of the joining system 10 of FIG. 1. Further, it will beunderstood that subsequent references to welding systems, heads or toolsare intended to refer generally to such elements for joining, includingfor example riveting or bonding processes.

[0076]FIG. 2 shows an alternative embodiment of a welding head 22. Incontradistinction to the welding head 22 of FIG. 1, a rotary drive 68′is provided to rotate the welding tool 32, not in the end portion of thesecond carrying segment 30, but in the region of the control means 42.The rotary motions of the rotary drive 68′ are transmitted to thewelding tool 32 by means of a belt drive 80. The belt drive 80 runsalong the elongated carrier 26. The elongated carrier 26 is formed inthe representation of FIG. 2 by two parallel arms, between whose endportions the welding tool 32 is rotatably mounted.

[0077]FIGS. 3 and 4 represent an embodiment of a holding means 66. Theholding means 66 comprises a housing 84, in turn comprising an opening86 facing downward in the joining direction. The holding means 66comprises two jaws 88A, 88B mounted with limited swingability on thehousing 84 and made of an essentially inelastic material. The jaws 88A,88B form a tongs, an element 36 being grasped between the ends of thejaws 88A, 88B with a predetermined force.

[0078] The jaws 88A, 88B are each connected in one piece with a leversegment 92A, 92B. With respect to axes 90A, 90B on which the jaws 88A,88B are mounted, the lever segments 92A, 92B extend in the respectiveother direction. The lever segments 92A, 92B are here bent off relativeto the joining direction 40, so that they overlap. By pressure on thelever segments 92A, 92B from above (in the representation of FIG. 3),the jaws 88A, 88B are consequently moved away from each other, releasingthe bolt 36. This is shown for the jaw 88A in FIG. 3. It may be seenthat the jaw 88A releases the bolt 36 completely in the directiontransverse to the joining direction 40 (that is, in FIG. 3, out of theplane of the paper). Consequently the holding means 66 with opened jaws88A, 88B can be moved transverse to the joining direction 40 andperpendicular to the plane of the jaws 88A, 88B without touching thebolt 36. The direction of motion of the jaws 88A, 88B in this operationis designated 93 in FIG. 4.

[0079] To actuate the lever segments 92A, 92B, an actuator 94 isprovided, preferably triggered electrically. The actuator 94 opens andcloses the jaws 88A, 88B actively in each instance. It will beunderstood that for this purpose the actuator 94 must be configured as atwo-directional drive.

[0080] Active actuation of the jaws 88A, 88B has the advantage that thebolt 36 can be held with a defined force (for example 20 newtons). Thederivation of the holding force from the elasticity of the severalfingers of the tongs, as in the prior art, is dispensed with.Consequently a definitely longer service life can be attained. Thedirection of actuation of the actuator 94 is shown at 96 in FIG. 3. Attheir ends, the jaws 88A, 88B are of such conformation that they cansecurely grasp the bolt 36 in question. For this purpose, it may beappropriate to place suitable adapters on the jaws 88A, 88B, in order tofit different bolts 36.

[0081] From the under side of the housing 94, as shown in FIG. 3, apositioning pin 98 extends. The positioning or contact pin 98 is rigidlyconnected to the housing 84. It serves, when a bolt 36 is picked up fromthe transfer station 46, to ensure that the bolt 36 will occupy adefined position in relation to the holding means 66, and as a stop toassume the axial forces in welding.

[0082] The two-directional active actuator can consist of a pneumatic orhydraulic drive. Preferably, however, it consists of a combination oftwo electromagnets, or of an unregulated linear motor on the ‘movingcoil’ or ‘moving permanent magnet’ principle. Further, it is possible toconfigure the actuator 94 as semi-active. Then the opening of the jaws88A, 88B is effected for example by an electromagnet. When this isswitched on, suitably arranged springs serve to ensure that a bolt 36will be grasped by the jaws 88A, 88B with a defined force.

[0083] For welding, the jaws 88A and/or 88B are supplied with weldingcurrent, conducted to the bolt 36. The defined force provides for asecure, low-wear passage of current. For this reason, it will beunderstood that the jaws 88A, 88B will be made of a conductive metal.The positioning pin 98, however, should be non-conductive, or insulatedfrom the housing 84.

[0084] Alternatively to an active or semi-active holding means 66, it ispossible also to provide jaws of elastic configuration, permitting alateral introduction of the bolt 36 between them (in the direction 93)and releasing them without substantial exertion of force upon motiontransverse to a welded-on bolt 36. In FIG. 3, the longitudinal axis ofthe holding means 66 is designated 100.

[0085] In FIGS. 5 and 6, an additional alternative embodiment of awelding tool 32 is shown. The welding tool 32 comprises a tool housing102 to which a linear motor 104 of a joining drive means 64 is fixed.The axis or centerline of the linear motor 104 is shown at 105. It isrepresented that the axis 100 of the holding means 66 and the axis 105of the linear motor 104 are spaced at a distance d from each other. Inthis way the holding means 66 is shifted out of the projection of thelinear motor 104 in joining direction. This makes it possible toposition the holding means 66, and therefore a held bolt 36, closer toan interfering wall or edge. Upon the whole, this enhances theflexibility of the welding head 22.

[0086] The linear motor 104 comprises an armature segment 106 connectedto a guide plate 108 extending transverse to the joining direction. Fromthe guide plate 108, two guide rods 110, 112 extend, arranged diagonallyin relation to the linear motor 104. The guide rods 110, 112 ensure thatthe guide plate 108 is guided free from tilt. From the under side of theguide plate 108, the holding means 66 extends. An actuator to actuatethe hold means 66 may for example be configured on top of the guideplate 108 or integrated therein.

[0087] In FIG. 6, it is shown that the carrier 26 is made up of acomparatively massive carrying arm 116 and a less massive tension arm118 extending parallel thereto. The welding tool 32 is mounted betweenthe arms 116, 118 along the axis of rotation 34. In FIG. 6, currentcables 120 to supply current to the jaws 88A, 88B are also indicated.

[0088] Another alternative conformation of a joining tool 32 is shown inFIG. 7. The welding tool 32 comprises a linear motor housing 122. At thetops of the guide rods 110, 112, flanges 123 are provided in eachinstance. Between the flanges 123 and the linear motor housing 122,compression springs 124 are arranged, configured around the guide rods110, 112. The linear motor 104 is consequently so pre-stressed by thecompression springs 124 that the guide plate 108 moved thereby islocated in the retracted, to wit not extended, position. In addition tothe compression springs 124 or alternatively thereto, an additionalcompression spring 126 may be provided inside of the linear motorhousing 122.

[0089] Further, it is shown that on top of the guide plate 108, a hingedmagnet 128 is articulated to an axis 130. The magnet 128 serves to pressthe lever segments 92A, 92B downward to open the jaws 88. In general,however, the lever segments 92 are pre-stressed towards the closedposition of the jaws 88 by means of a tension spring 132.

[0090]FIG. 8 shows a first embodiment of a transfer station 46 of thefeeding means 44. At the transfer station 46, two opposed sensors 136(for example a light barrier) are provided, detecting whether there is abolt 36 in the transfer station 46 or not.

[0091] The feeding means 44 consists essentially of a tube or hose 138,bent off inward in the region of the transfer station 46. The bolts 36are fed shank first from the individualizing device 52 through thefeeding means 44. Consequently the head of the bolt 36 will strike therolled edge of the tube 138 and remain so in the transfer station 46.Thus the shank of the bolt 36 protrudes from the tube 138.

[0092] The holding means 66 can now be run with opened jaws 88A, 88B allthe way to the bolt 36 and grasp it. Then the holding means 66 is swungback again, out of the plane of the paper in the representation of FIG.8. It will be understood that at the transfer station 46, a suitablelateral recess must be provided in the tube 138, though not explicitlyshown in FIG. 8.

[0093] An alternative embodiment of a transfer station 46′ is shown inFIG. 9. In this embodiment a tube 138′ of the feeding means 44′ is opentowards the end. At a transfer housing 140, two clamping jaws 142 arerotatably mounted. The jaws 142 are pre-stressed by means of two springs144 into a position where their inner sides block the exit of a bolt 36from the tube 138′. The bolt 36 is braked thereby upon being fed. Here apositioning lever 146 is swung laterally out of the representation shownin FIG. 9 to let the bolt 36 through. Then the positioning lever 146 isswung, as indicated at 147. Thus the bolt 36 presses the jaws 142A, 142Bapart and is shifted away from the tube 138′ until the head of the bolt36 snaps into an annular recess 148. The annular recess 148 is formed bythe inner sides of the jaws 142A, 142B. In this position, the bolt 36 isdefinitely held with a certain force. The holding means 66 may, as inFIG. 8, grasp the shank of the bolt 36 and pull it laterally out of theannular recess 148.

[0094] Over the embodiment of FIG. 8, this embodiment has the advantagethat the bolt 36 is in a defined position in the transfer position 46′,and is held with a defined force, so that a secure hold on the bolt 36by the holding means 66 is ensured. It will be understood that at thetransfer station 46′ also, suitable sensors may be provided to detect abolt 36 in the transfer position.

[0095] A third embodiment of a transfer station 46″ is shown in FIGS. 10and 11. In this embodiment, the bolts 36 are conveyed by way of a tube138″ into a bolt receptacle 154 of a swingable rotational segment 152.The segment 152 is rotatable about an axis 153 oriented transverse tothe axis of the tube 138″ and transverse to the orientation of the bolt36 in the transfer position.

[0096] In FIGS. 10 and 11, the segment 152 is in a transfer position. Inthis position, a pneumatic cylinder 156 serves to push the bolt 36 bymeans of a plunger 158 between two tension jaws 160, between which thebolt 36 is then hold in a defined manner. Then the segment 152 is turnedback to pick up another bolt 36 in the receiving position shown dotted,flush with the tube 138″. This embodiment has the advantage that thebolts 36 can be conveyed at high speed through the tube 138″. Henceshort cycle periods can be achieved.

[0097] Another embodiment of a welding head according to the inventionis generally designated 170 in FIG. 12. The welding head 170 comprises,at the anterior end of the carrier 26, a welding tool 171 comprisingonly a housing rotatably mounted on the carrier 26 and a holding means172 fixed thereto. The welding tool 171 is not provided with a weldingdrive motor, in particular not a linear motor.

[0098] The holding means 172 comprises two jaws 174 between which a bolt36 is so held that it is oriented tangential to a circumference aroundthe axis of rotation 34. In other words, a joining operation does notoccur along a rectilinear motion, but along a circular path. Thecorresponding direction of guidance is indicated in FIG. 12 as a partialcircle 176.

[0099] In this embodiment, a rotary drive 175 serves as joining drivemeans, arranged in the region of the control means 42. Rotary motions ofthe drive 175 are transmitted by a belt drive 80 to the welding tool171. It will be understood that the rotary drive 175 is preferably anelectric precision step motor with which the difficult movements of thebolt 36 can be executed during a bolt welding operation. The rotarydrive 175 thus serves simultaneously also as loading drive, being swungso as to pick up one new bolt 36 at a time from a transfer station 180of a feeding means 178.

[0100] In the feeding means 178, the bolts 36 are not fed successivelybut side by side, in such manner that the holding means 172 can graspthe bolts 36 transverse to their own extent. It will be understood thatthe feeding means 178 may either comprise suitable means of convertingthe lengthwise motion out of the individualizing device 52 into thetransverse orientation shown in FIG. 12, or alternatively it is possibleto feed the bolts 36 out of the individualizing device 52 already intransverse position.

[0101] Further, in FIG. 12 schematically a magazine 186 provided on thecarrier 26 is provided. The magazine 186 may serve as supply magazinefor a plurality of bolts 36, then to be transferred by means of asuitable integrated individualizing device to the feeding means 178, orto the transfer station 180. It will be understood that such a magazinemay also be employed in the embodiments of FIGS. 1 to 11 instead of astationary individualizing device 52 or in addition thereto.

The invention claimed is:
 1. A joining system head comprising: holdingmeans for holding an element to be joined to a part; joining drive meansfor moving the holding means along a joining direction for joining;feeding means for feeding elements to the joining system head, thefeeding means including a transfer station; control means forcontrolling the joining drive means, the control means being arranged atthe joining system head spatially distanced from the holding means andthe joining drive means so that the holding means and the joining drivemeans define a joining tool of small dimensions; and means for passingon the elements fed to the transfer station of the feeding means.
 2. Thejoining system head according to claim 1, further comprising aprojecting elongated carrier, the joining tool being mounted on an endportion of the projecting elongated carrier.
 3. The joining system headaccording to claim 2, wherein the joining tool is movably mounted on theend portion of the carrier and further comprising a loading drive meansis designed to move the joining tool to the transfer station in order topass on an element to the holding means.
 4. The joining system headaccording to claim 3, wherein the joining tool is rotatably mounted onthe end portion of the carrier and the loading drive means is designedto rotate the joining tool all the way to the transfer station.
 5. Thejoining system head according to claim 3, wherein the loading drivemeans comprises a motor arranged on the end portion of the carrier. 6.The joining system head according to claim 3, wherein the loading drivemeans comprises a motor arranged in the vicinity of the control meansand a transmission that transmits motions of the motor to the joiningtool.
 7. The joining system head according to claim 6, wherein the motoris a rotary motor and the transmission is a tension means transmission.8. The joining system head according to claim 1, wherein the joiningdrive means consists of a linear electric motor.
 9. The joining systemhead according to claim 8, wherein the longitudinal axis of the joiningdrive means and the longitudinal axis of the holding means are distancedparallel from each other.
 10. The joining system head according to claim1, wherein the holding means comprises a plurality of jaws arrangedaround the longitudinal axis of the holding means and movable towardsand away from each other, in each instance to hold or release anelement.
 11. The joining system head according to claim 10, wherein theholding means comprises two jaws.
 12. The joining system head accordingto claim 10, wherein the jaws are movable away from each other farenough so that the holding means can release the element by being drawnoff from the element oblique to the joining direction.
 13. The joiningsystem head according to claim 12, wherein the jaws are movable awayfrom each other far enough so that the holding means can release theelement by being swung away from the element about an axis of rotationoriented transverse to the joining direction.
 14. The joining systemhead according to claim 10, further comprising a jaw actuator, activelymoving the jaws.
 15. The joining system head according to claim 10,wherein the jaws are passively movable relative to each other.
 16. Thejoining system head according to claim 2, wherein the transfer stationis arranged on the elongated carrier.
 17. The joining system accordingto claim 1, further comprising a robot movable on at least twocoordinate axes and a joining system head fixed to the robot.
 18. Thejoining system according to claim 17, further comprising a stationaryindividuating means conveying individuated elements all the way to thefeeding means of the joining system head.
 19. The joining system headaccording to claim 1, wherein the feeding means comprises a magazine forelements.
 20. A joining system comprising: an element; a holder operableto at least temporarily retain the element during joining; a transferstation spaced apart from the holder; and a feeder unit spaced apartfrom but connected to the transfer station, the feeder unit operablytransferring the element to the transfer station where its movement isinterrupted before being further transferred to the holder.
 21. Thesystem of claim 20, wherein: the feeder unit comprises a feed deviceoperably individualizing a bulk plurality of the element; furthercomprising an elongated tube connecting the feed device to the transferstation; and the feed device is substantially stationary and at least aportion of the tube is movable with the transfer station which ismovable.
 22. The system of claim 21, further comprising compressed aircauses each individualized element to move through the tube.
 23. Thesystem of claim 20, further comprising an electromagnetic driveroperably moving the element relative to the holder.
 24. The system ofclaim 23, wherein the driver is a linear motor.
 25. The system of claim20, further comprising an articulated robot operably moving the holder.26. The system of claim 20, further comprising a welding arc createdadjacent at least one of: the element and the holder.
 27. The system ofclaim 20, wherein the element is transferred to the holder in at leasttwo discrete steps.
 28. The system of claim 20, wherein the feeder unitis stationary and the transfer station is movable.
 29. The system ofclaim 20, wherein the element includes an elongated shank and anenlarged head.
 30. The system of claim 20, wherein the holder isrotatable relative to the transfer station, the holder automaticallygrasps the element and moves it from the transfer station and then theholder rotates the element into a joining position.
 31. A joining systemcomprising: an element holder; an automatic element driver locatedadjacent the holder; and a controller connected to and operablycontrolling the driver; wherein the controller is movable with theholder and the driver in at least one operating condition; and whereinthe controller is spaced apart from the holder and the driver such thatthe holder and the driver are movable independently from the controllerin another operating condition.
 32. The system of claim 31, furthercomprising a depositable element operably moved relative to the holderby the driver.
 33. The system of claim 32, further comprising creating awelding arc from the element when the element is retained by the holder.34. The system of claim 32, wherein the element is transferred to theholder in at least two discrete steps.
 35. The system of claim 31,further comprising an elongated member separating the controller fromthe holder and the driver.
 36. The system of claim 35, wherein theentire holder is movable relative to the elongated member.
 37. Thesystem of claim 31, further comprising an articulated robot operablymoving the holder.
 38. The system of claim 37, further comprising: ametallic element; a workpiece having an opening; the robot having astationary base located on one side of the opening of the workpiece; theholder being insertable through the opening of the workpiece to join theelement to the workpiece on an opposite side of the opening from thestationary base.
 39. The system of claim 31, wherein the driver includesan electromagnetic device.
 40. The system of claim 31, wherein thedriver is a linearly moving electric motor.
 41. A welding apparatuscomprising: multiple depositable elements; a robot having at least onejoint between elongated, structural and movable members; a welding toolcoupled to one of the structural members by a second joint, the secondjoint allowing automatic movement of the tool independent from thestructural members, the tool operably welding the elements; and acontrol unit connected to the tool, the control unit being movable withat least one of the structural members and the tool being movableindependently from the control unit.
 42. The apparatus of claim 41,wherein the welding tool comprises a holder operably holding at leastone of the elements at a time, and an electromagnetic driver operablymoving the element relative to the holder.
 43. The apparatus of claim42, wherein the driver is a linear motor.
 44. The apparatus of claim 41,further comprising a feeder and a transfer station, the feeder operablysequentially feeding the elements to the transfer station, the transferstation being movable with at least one of the members.
 45. Theapparatus of claim 44, wherein the element is transferred to the holderin at least two discrete steps.
 46. The apparatus of claim 44, whereinthe welding tool includes an element holder, the holder is rotatablerelative to the transfer station, the holder automatically grasps theelement and moves it from the transfer station and then the holderrotates the element into a joining position.
 47. The apparatus of claim45, further comprising a welding arc being created from at least one ofthe elements when in the tool.
 48. A welding machine comprising: a robothaving at least one joint between elongated structural members; anarc-welding tool being coupled to one of the structural members; adepositable element-transfer station movable with at least one of thestructural members, and the tool being independently movable from thetransfer station; a depositable element-feeder; and a tube connectingthe feeder to the transfer station, the feeder being substantiallystationary and at least a portion of the tube being movable with thetransfer station.
 49. The machine of claim 48, wherein the arc-weldingtool includes a linear depositable element-driver and a set ofdepositable element retaining jaws.
 50. The machine of claim 49, furthercomprising an automatic actuator operably rotating the arc-welding toolrelative to the structural members.
 51. The machine of claim 49, whereinthe driver is a linear motor.
 52. The machine of claim 48, furthercomprising compressed air causing individualized depositable elements tomove through the tube.
 53. The machine of claim 48, further comprising aweldable element transferred to the holder in at least two discretesteps.
 54. A fastening apparatus comprising: multiple depositableelements; a robot having at least one joint between elongated structuralmembers; a fastening tool being coupled to one of the structuralmembers; and a feeder unit operably containing the elements; theelements being automatically and individually transferred from thefeeder unit to the tool in at least two discrete steps to allow at leasta first one of the elements to be fastened by the tool simultaneouslywith feeding of at least a second one of the subsequent elements. 55.The apparatus of claim 54, wherein the tool includes a driver operablylinearly moving the depositable elements and a set of jaws operablyretaining the depositable elements.
 56. The machine of claim 55, furthercomprising an automatic actuator operably rotating the tool relative tothe structural members.
 57. The machine of claim 55, wherein the driveris a linear motor.
 58. The apparatus of claim 54, wherein the elementsare elongated and weldable parts.
 59. The apparatus of claim 54, whereinthe elements are rivets.
 60. The apparatus of claim 54, furthercomprising a welding arc created adjacent at least one of: one of theelements and the tool.
 61. The apparatus of claim 54, wherein at least aportion of the feeder unit is stationary when the structural members areautomatically moved.
 62. A joining system comprising: a robot having atleast one joint between elongated structural members; joining toolcoupled to one of the structural members by a second joint; and anelectrical control unit connected to the tool, the control unit beingmovable with at least one of the structural members and the tool beingmovable independently from the control unit.
 63. The system of claim 62,further comprising a set of individual metallic elements welded by thetool.
 64. The system of claim 63, wherein the tool includes a holder andan electromagnetic driver which advances the elements relative to theholder, the tool is movable in a manner to allow the holder to releasethe welded-on element in a direction substantially transverse to awelding direction.
 65. The system of claim 62, further comprising arotary drive unit operable to rotate the tool at the second joint. 66.The system of claim 65, further comprising an elongated drivetransmission coupling the rotary drive unit to a member associated withat least one of the tool and the second joint, the rotary drive unitbeing remotely located away from the tool and the second joint, and therotary drive unit being movable with at least one of the structuralmembers.
 67. The system of claim 62, further comprising a set of rivetslinearly inserted by the tool.
 68. The system of claim 62, furthercomprising depositable elements and workpieces, wherein the tooloperably bonds the elements to the workpieces.
 69. The system of claim62, further comprising an electric step motor operably rotating the toolat the second joint.